This project involves study of the anatomical properties and organization of cells in the visual system of primates, with emphasis on the retina and the visual cortex. The studies include (1) the pattern distribution of cones in the retinas of human donors with a diagnosis of diabetic retinopathy and (2) the anatomical association of outer-retinal cells selectively stained with tissue-reactive dyes. Evidence of a cone population with a point pattern resembling that of cones selectively stained by tissue-reactive dyes has been obtained in initial studies of the retina of human eye donors with a history of diabetes. Although such dyes were not injected in the eyes of these donors, in vitro staining with more conventional dyes has shown a differential labeling of the receptors, in which some cones appear more densely stained than others, with a point pattern similar to that of the blue-sensitive cones of primate retina. A systematic study continues on the anatomical association at the light-microscope level of blue cones and horizontal and bipolar cells that have been selectively stained by several tissue-reactive dyes in the macaque retina. The results have provided information on the probable retinal circuitry of the blue-sensitive cone pathway of primate retina.